It is desirable to understand electrostatic phenomena observed with moving, slightly conductive dielectric webs passing over grounded metallic conveyor rollers. For example, it would be desirable in connection with determining how natural charge limitation occurs in the moving web. To obtain such an understanding, it is important to know how net charge is distributed on the web. If the web has some conductivity so that charge can move on the web, then the distribution will be dynamic, i.e. it will change as the environment through which it passes changes. In such a case, the charge must be analyzed taking into account all the forces which can influence charge movement.
Charge distribution in the lengthwise direction of the web, i.e. in the direction of conveyance of the web over the roller, and apparatus for measuring such lengthwise distribution is described in the article entitled "Segmented Roller: A Device for Measuring Charge Density on a Moving Conducting Web" published in Journal of Electrostatics, Vol. b 24, pages 21-32 (1989). While the apparatus described in that article is capable of measuring lengthwise charge distribution, no capability existed for measuring lateral charge distribution. However, it is important in the context of understanding electrostatic phenomena of moving webs to know the lateral distribution of charge on the web.
It is therefore an object of the present invention to provide apparatus capable of measuring lateral charge distribution on a moving web.